121 research outputs found
Electrons in an annealed environment: A special case of the interacting electron problem
The problem of noninteracting electrons in the presence of annealed magnetic
disorder, in addition to nonmagnetic quenched disorder, is considered. It is
shown that the proper physical interpretation of this model is one of electrons
interacting via a potential that is long-ranged in time, and that its technical
analysis by means of renormalization group techniques must also be done in
analogy to the interacting problem. As a result, and contrary to previous
claims, the model does not simply describe a metal-insulator transition in
() dimensions. Rather, it describes a transition
to a ferromagnetic state that, as a function of the disorder, precedes the
metal-insulator transition close to . In , a transition from a
paramagnetic metal to a paramagnetic insulator is possible.Comment: 13 pp., LaTeX, 2 eps figs; final version as publishe
Progress on nuclear reaction rates affecting the stellar production of 26Al
The radioisotope 26Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch stars; to massive and very massive stars, both their Wolf–Rayet winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several reactions affect the production of 26Al in these astrophysical objects, including (but not limited to) 25Mg(p, ¿)26Al, 26Al(p, ¿)27Si, and 26Al(n, p/a). Extensive experimental effort has been spent during recent years to improve our understanding of such key reactions. Here we present a summary of the astrophysical motivation for the study of 26Al, a review of its production in the different stellar sites, and a timely evaluation of the currently available nuclear data. We also provide recommendations for the nuclear input into stellar models and suggest relevant, future experimental work.Postprint (published version
Microscopic nonequilibrium theory of double-barrier Josephson junctions
We study nonequilibrium charge transport in a double-barrier Josephson
junction, including nonstationary phenomena, using the time-dependent
quasiclassical Keldysh Green's function formalism. We supplement the kinetic
equations by appropriate time-dependent boundary conditions and solve the
time-dependent problem in a number of regimes. From the solutions,
current-voltage characteristics are derived. It is understood why the
quasiparticle current can show excess current as well as deficit current and
how the subgap conductance behaves as function of junction parameters. A
time-dependent nonequilibrium contribution to the distribution function is
found to cause a non-zero averaged supercurrent even in the presence of an
applied voltage. Energy relaxation due to inelastic scattering in the
interlayer has a prominent role in determining the transport properties of
double-barrier junctions. Actual inelastic scattering parameters are derived
from experiments. It is shown as an application of the microscopic model, how
the nature of the intrinsic shunt in double-barrier junctions can be explained
in terms of energy relaxation and the opening of Andreev channels.Comment: Accepted for Phys. Rev.
Immune reconstitution inflammatory syndrome in HIV infected late presenters starting integrase inhibitor containing antiretroviral therapy
Background: Integrase inhibitors (INI) induce a rapid decline of HIV-RNA in plasma and CD4+ T-cell recovery in blood. Both characteristics are also associated with immune reconstitution inflammatory syndrome (IRIS). Whether the use of INI-containing combination antiretroviral therapy (cART) increases the risk of IRIS is being questioned. Methods: Study within the Dutch ATHENA HIV observational cohort. HIV-1 infected late presenters initiating cART after March 2009 were included if they had <200 CD4+ T-cells per μL and were diagnosed with an opportunistic infection. IRIS was defined either according to the criteria by French et al. (IRISFRENCH) or by a clinical IRIS diagnosis of the physician (IRISCLINICAL). The primary outcomes were the association between INI and the occurrence of IRISFRENCH and IRISFRENCH+CLINICAL in multivariable logistic regression. Findings: 672 patients with a median CD4+ T-cell count of 35 cells per μL were included. Treatment with INI was independently associated with IRISFRENCH as well as IRISFRENCH+CLINICAL (OR 2·43, 95%CI:1·45–4·07, and OR 2·17, 95%CI:1·45–3·25). When investigating INI separately, raltegravir (RAL) remained significantly associated with IRISFRENCH (OR 4·04 (95%CI:1·99-8·19) as well as IRISFRENCH+CLINICAL (OR 3·07, 95%CI:1·66-5·69), while dolutegravir (DTG) became associated with IRISFRENCH+CLINICAL after it replaced RAL as preferred INI in the cohort after 2015 (OR 4·08, 95%CI:0·99-16·82, p=0·052). Too few patients used elvitegravir to draw meaningful conclusions. Steroid initiation for IRIS was more likely in those who initiated INI versus in those who did not, but no increased hospital (re)admission or mortality rates were observed. Interpretation: In HIV late presenters from a resource rich setting, INI based treatment initiation increased the risk of IRIS. This was observed for RAL and DTG when being initiated as preferential INI in the presence of specific AIDS-conditions, indicative of channeling bias. Although we controlled for all relevant measured confounders, we cannot exclude that the observed association is partially explained by residual confounding. INI use was not associated with mortality nor hospitalization. Therefore, our observation is no reason to avoid INI in late presenters. Funding: Th
Nonequilibrium electron cooling by NIS tunnel junctions
We discuss the theoretical framework to describe quasiparticle electric and
heat currents in NIS tunnel junctions in the dirty limit. The approach is based
on quasiclassical Keldysh-Usadel equations. We apply this theory to diffusive
NIS'S tunnel junctions. Here N and S are respectively normal metal and
superconductor reservoirs, I is an insulator layer and S' is a nonequilibrium
superconducting lead. We calculate the quasiparticle electric and heat currents
in such structures and consider the effect of inelastic relaxation in the S'
lead. We find that in the absence of strong relaxation the electric current and
the cooling power for voltages are suppressed. The value of this
suppression scales with the diffusive transparency parameter. We ascribe this
suppression to the effect of backtunneling of nonequilibrium quasiparticles
into the normal metal.Comment: 12 pages, 6 figures, proceedings, to be published in JLT
A somatic-mutational process recurrently duplicates germline susceptibility loci and tissue-specific super-enhancers in breast cancers
Somatic rearrangements contribute to the mutagenized landscape of cancer genomes. Here, we systematically interrogated rearrangements in 560 breast cancers by using a piecewise constant fitting approach. We identified 33 hotspots of large (>100 kb) tandem duplications, a mutational signature associated with homologous-recombination-repair deficiency. Notably, these tandem-duplication hotspots were enriched in breast cancer germline susceptibility loci (odds ratio (OR) = 4.28) and breast-specific 'super-enhancer' regulatory elements (OR = 3.54). These hotspots may b
FUV and X-ray absorption in the Warm-Hot Intergalactic Medium
The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas
collapsing in large-scale filaments and probably harbours a substantial
fraction of the baryons in the local Universe. Absorption-line measurements in
the ultraviolet (UV) and in the X-ray band currently represent the best method
to study the WHIM at low redshifts. We here describe the physical properties of
the WHIM and the concepts behind WHIM absorption line measurements of H I and
high ions such as O VI, O VII, and O VIII in the far-ultraviolet and X-ray
band. We review results of recent WHIM absorption line studies carried out with
UV and X-ray satellites such as FUSE, HST, Chandra, and XMM-Newton and discuss
their implications for our knowledge of the WHIM.Comment: 26 pages, 9 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 3; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Superstripes and complexity in high-temperature superconductors
While for many years the lattice, electronic and magnetic complexity of
high-temperature superconductors (HTS) has been considered responsible for
hindering the search of the mechanism of HTS now the complexity of HTS is
proposed to be essential for the quantum mechanism raising the superconducting
critical temperature. The complexity is shown by the lattice heterogeneous
architecture: a) heterostructures at atomic limit; b) electronic heterogeneity:
multiple components in the normal phase; c) superconducting heterogeneity:
multiple superconducting gaps in different points of the real space and of the
momentum space. The complex phase separation forms an unconventional granular
superconductor in a landscape of nanoscale superconducting striped droplets
which is called the "superstripes" scenario. The interplay and competition
between magnetic orbital charge and lattice fluctuations seems to be essential
for the quantum mechanism that suppresses thermal decoherence effects at an
optimum inhomogeneity.Comment: 20 pages, 3 figures; J. Supercon. Nov. Mag. 201
Plasma lipid profiles discriminate bacterial from viral infection in febrile children
Fever is the most common reason that children present to Emergency Departments. Clinical signs and symptoms suggestive of bacterial infection are often non-specific, and there is no definitive test for the accurate diagnosis of infection. The 'omics' approaches to identifying biomarkers from the host-response to bacterial infection are promising. In this study, lipidomic analysis was carried out with plasma samples obtained from febrile children with confirmed bacterial infection (n = 20) and confirmed viral infection (n = 20). We show for the first time that bacterial and viral infection produces distinct profile in the host lipidome. Some species of glycerophosphoinositol, sphingomyelin, lysophosphatidylcholine and cholesterol sulfate were higher in the confirmed virus infected group, while some species of fatty acids, glycerophosphocholine, glycerophosphoserine, lactosylceramide and bilirubin were lower in the confirmed virus infected group when compared with confirmed bacterial infected group. A combination of three lipids achieved an area under the receiver operating characteristic (ROC) curve of 0.911 (95% CI 0.81 to 0.98). This pilot study demonstrates the potential of metabolic biomarkers to assist clinicians in distinguishing bacterial from viral infection in febrile children, to facilitate effective clinical management and to the limit inappropriate use of antibiotics
Partially methylated domains are hypervariable in breast cancer and fuel widespread CpG island hypermethylation
Global loss of DNA methylation and CpG island (CGI) hypermethylation are key epigenomic
aberrations in cancer. Global loss manifests itself in partially methylated domains (PMDs)
which extend up to megabases. However, the distribution of PMDs within and between
tumor types, and their effects on key functional genomic elements including CGIs are poorly
defined. We comprehensively show that loss of methylation in PMDs occurs in a large
fraction of the genome and represents the prime source of DNA methylation variation. PMDs
are hypervariable in methylation level, size and distribution, and display elevated mutation
rates. They impose intermediate DNA methylation levels incognizant of functional genomic
elements including CGIs, underpinning a CGI methylator phenotype (CIMP). Repression
effects on tumor suppressor genes are negligible as they are generally excluded from PMDs.
The genomic distribution of PMDs reports tissue-of-origin and may represent tissue-specific
silent regions which tolerate instability at the epigenetic, transcriptomic and genetic level
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